Miliaria Profunda

The rarest and deepest form of miliaria. Sweat duct obstruction and rupture occur at the dermo epidermal junction and upper dermis, so sweat leaks into the dermis.

• It usually follows repeated attacks of miliaria rubra, mainly in tropical climates and in people who sweat heavily and chronically, such as military personnel, outdoor workers and recent arrivals in the tropics. It is much less common in temperate climates.
• Because the ducts are obstructed deep in the skin, sweat production over the affected area is reduced or absent (anhidrosis), and a large affected area causes heat intolerance and heat retention. The extreme form is called tropical anhidrotic asthenia, with fatigue, weakness, dizziness, headache, palpitations, dyspnoea and exhaustion, and a risk of heat exhaustion and heat stroke.
• Compensatory facial and axillary hyperhidrosis may be present, with sparing of those regions from the eruption.
• Patients with chronic skin disease that impairs sweat flow (ichthyosis, atopic dermatitis), and those taking anticholinergic drugs, are at greater risk of heat illness.

• Flesh coloured or pale, firm, 1 to 3 mm, non-itchy papules on the trunk and extremities, which resemble goose flesh. They are not follicular. They appear after sweating and become more obvious with heat, and they disappear when the skin cools.
• The face, axillae and palms are generally spared.
• Overheating causes malaise, dizziness, headache, fatigue, tachycardia and raised temperature, because the body cannot lose heat through sweat.
• Differential diagnosis: miliaria rubra, keratosis pilaris, lichen nitidus, cholinergic urticaria, goose flesh from cold, folliculitis, milia, and eruptions from drugs.
• Red flags: temperature of 40 C or more, confusion, absent sweating despite heat, syncope, cramps, vomiting or collapse (heat stroke).
• Complications: heat exhaustion, heat stroke, chronic fatigue, secondary infection, and reduced ability to work in hot climates.

• Clinical, based on the persistent firm papules, the history of earlier miliaria rubra, and heat intolerance.
• Confirm reduced sweating with a sweat test (the iodine starch or quinizarin test, or thermoregulatory sweat test) in unclear cases.
• Biopsy shows a ruptured duct with inflammation at the dermo epidermal junction and periductal infiltrate.
• In patients with heat symptoms measure core temperature, electrolytes, urea, creatinine, creatine kinase, liver tests and glucose.

• Strict cooling and avoidance of sweating is the cornerstone:
  • Stay in a cool, air conditioned environment, and avoid exertion in hot conditions, until the sweat glands recover (weeks, sometimes 2 to 3 months).
  • Wear light, loose cotton clothing, and avoid occlusion.
  • Use cool showers and wet cloths for heat relief.
  • Drink adequate fluids, and replace salt after sweating.
• Topical therapy:
  • Anhydrous lanolin applied 2 to 3 times daily to open obstructed ducts. Evidence is limited, but it is widely used.
  • Hydrocortisone 1% cream twice daily for 3 to 5 days for any inflamed areas.
• Systemic therapy (evidence is limited and for specialist use):
  • Vitamin C (ascorbic acid) 1 g orally daily for 3 to 4 weeks, which may reduce duct obstruction.
  • Oral isotretinoin at low dose (0.5 mg/kg per day) for several weeks has been used in resistant disease, with strict pregnancy prevention.
• Heat exhaustion or heat stroke: remove clothing, spray with cool water and fan, place ice packs on the neck, axillae and groin, give oral fluids if alert, give intravenous 0.9% sodium chloride 1 to 2 L over 1 to 2 hours adjusted to response, and arrange emergency transfer. Aim for core temperature below 39 C within 30 minutes.
• Review drugs that reduce sweating (anticholinergics, antihistamines, tricyclic antidepressants, topiramate, zonisamide) with the prescriber.
• Prevention: acclimatise to hot conditions gradually, treat miliaria rubra promptly, and avoid repeated sweating episodes in hot and occlusive conditions.
• Special groups:
  • Military and outdoor workers: remove from heat exposure until sweating recovers, and advise a graded return.
  • Pregnancy: use cooling, lanolin and brief hydrocortisone. Avoid isotretinoin.
  • Children: cooling, lanolin and light clothing, with careful watch for heat illness.
  • Elderly: higher risk of heat illness, and a lower threshold for assessment.
• Follow up: review every 2 to 4 weeks until papules resolve and sweating returns. Refer to dermatology or occupational health for persistent anhidrosis, or recurrent heat illness.